Re: [PATCH] x86, sched: Allow NUMA nodes to share an LLC on Intel platforms

[Dave Hansen]

On 2/10/21 12:05 AM, Peter Zijlstra wrote:
>> +	if (IS_ENABLED(CONFIG_NUMA))
>> +		set_cpu_bug(c, X86_BUG_NUMA_SHARES_LLC);
>>  }
> This seens wrong too, it shouldn't be allowed pre SKX. And ideally only
> be allowed when SNC is enabled.

Originally, this just added a few more models to the list of CPUs with
SNC.  I was hoping for something a bit more durable that we wouldn't
have to go back and poke at every year or two.

> Please make this more specific than: all Intel CPUs. Ofcourse, since you
> all knew this was an issue, you could've made it discoverable
> _somewhere_ :-(

You're totally right, of course.  The hardware could enumerate SNC as a
feature explicitly somewhere.  But, that's a little silly because all of
the information that it's enumerating about the CPU caches and NUMA
nodes present and correct is *correct*.  The secondary information would
only be for the CPU to say, "yeah, I'm really sure about that other stuff".

I think this sanity check has outlived its usefulness.